1. Field of the Invention
The present invention relates to a method for biodegrading a chloroethylene compound by the use of microorganisms derived from intestines of termites. More specifically, it relates to a biodegradation method useful for the purification of sewage or waste water containing trichloroethylene (TCE), a method for remediating a soil by the utilization of the microorganisms, and a method for obtaining the microorganisms useful for the biodegradation of TCE.
Furthermore, the present invention relates to a biodegradation method using microorganisms in which an chlorinated organic compound degrading activity can be induced with an inducer.
2. Related Background Art
In recent years, various environmental inspections have reported that harmful and less degradable aromatic chemical substances have been detected, and in consequence, much attention has now been paid to environmental pollution with these substances. The influence of these substances on ecological systems is feared.
Therefore, in order to prevent pollution with these less degradable chemical substances, it is required to rapidly develop a technique by which these substances are inhibited from getting into the environment. For example, it is strongly desired to establish a technique by which the less degradable harmful substances can be effectively removed from sewage or waste water. Furthermore, the pollution of a soil with the less degradable harmful substances not only hinders the reutilization of the soil but also causes further escalation of the pollution due to the running of the pollutant into groundwater, which is a serious social problem. Therefore, it is strongly desired to establish a technique by which the escalation of the pollution with the less degradable chemical substances can be prevented and the polluted environment can be remediated.
In particular, TCE is an chlorinated organic compound which has been used in IC industries, dry cleaning and the like, and it is a carcinogen. Thus, the environmental pollution with TCE inclusive of the problem of the soil pollution caused by the pollution of groundwater is a serious social problem. Accordingly, the removal and the degradation of TCE contained in the environment, the purification of sewage or waste water containing TCE, and the remediation of the polluted soil are important themes from the viewpoint of environmental protection.
As a removal treatment and a degradation treatment of TCE, there are an adsorption treatment using active carbon, a degradation treatment utilizing light or heat, and the like. However, a biodegradation treatment using microorganisms is attracting attention from the standpoints of cost and operability.
There is a technique by which the function of microorganisms in a soil is utilized to degrade pollutants in the soil and to thereby eliminate the environmental pollution, and this technique is called bioremediation, because of remediating the soil by the use of the microorganisms. Hence, it can be expected that the bioremediation technique is applied to the remediation of polluted soils such as the vacant lot of a semiconductor manufacturing factory, a site of a metal processing factory, the vacant lot of a chemical plant, and the like.
However, there are not many reports that microorganisms having a TCE degrading ability have been isolated. Examples of the microorganisms having TCE degrading ability are limited, and they include Welchia alkenophila sero 5 (U.S. Pat. No. 4,877,736, ATCC53570), Welchia alkenophila sero 33 (U.S. Pat. No. 4,877,736, ATCC53571), Methylosinus trichosprium OB3b [Whitenbury R. J., Gen. Microbiol, Vol. 61, pp. 205-218 (1970)], Acinetobacter sp. G4 [Nelson M J K et al., Appl. Eviron. Microbiol., Aug., pp. 383-384 (1986); Folsom B. R. et al., Appl. Eviron. Microbiol., May, pp. 1279-1285 (1990); and U.S. Pat. No. 4,925,802, ATCC53617; this bacterium has first belonged to Pseudomonas cepacia but then changed to Acinetobacter sp.], Methylomonas sp. MM2 [Henry S M et al., Appl. Environ. Microbiol., Jan., pp. 236-244 (1991)], Alcaligenes denitrificans ssp. Xylosoxidsans JE75 [Ewers J. et al., Arch. Microbiol., Vol. 154, pp. 410-413 (1990)], Alcaligenes eutrophus JMP 134 [Harker A R & Kim Y. Appl. Environ. Microbiol., Apr., pp. 1179-1181 (1990)], Pseudomonas putida F1 [Gibson D T et al., Biochem., Vol. 7, pp. 2653-2662 (1968); Wackett L. P. & Gibson D. T., Appl. Environ. Microbiol, July, pp. 1703-1708 (1988)], Mycobacterium vaccse JOB5 [Beam H. W. & Perry J. J., J. Gen. Microbiol., Vol. 82, pp. 163-169 (1974); Wackett L. P. et al., Appl. Environ. Microbiol., Nov., pp. 2960-2964 (1989), ATCC29678], Nitrosomonas europaea [Arciero D. et al., Biochem. Biophys. Res. Comm., Vol. 159, pp. 640-643 (1989)], Pseudomonas fluoescens PFL12 [Vandenbergh P. A. & Kunka B. S., Appl. Environ. Microbiol., Oct., pp. 2578-2579 (1988)], Lactobacillus fuctivorans RE [Kunkee, Int. J. Syst. Bact., Vol. 30, pp. 313-314 (1980), J. Appl. Bact., Vol. 34, pp. 541-545 (1971)], Lactobacillus vaginalis sp. nov. [Embley T. M. et al., Int. J. Syst. Bacteriol., Vol. 39, pp. 368-370 (1989), ATCC49540], and Methylosinus trichosprium (Japanese Patent Application Nos. 2-92274 and 3-292970).
In addition, none of the presently known bacteria can meet the practical requirements for the TCE degradation method using the microorganisms and do not possess sufficient degrading ability.
Particularly in the case the microorganisms are used in the soil, it must be considered that the treatment is carried out in a specific environment, i.e. in the soil. The microorganisms to be used are required to have a sufficient TCE degrading activity and to effectively show this activity in the soil, but in the conventionally known bacteria, these points are not sufficient.
Nowadays, the acquisition of the bacteria which can meet practically necessary characteristics is strongly desired.
Such microorganisms are those which preferably have sufficient TCE degrading ability, are different from known bacteria in growth conditions and the like, can be applied to a wide range, are rich in utilizable morphology, and particularly can be effectively utilized in the specific environment of the soil. Examples of such additional requirements include drug resistance and an ability to utilize sucrose.
For example, in the case that the waste water containing TCE is treated, it is required that the microorganisms to be used have a TCE degrading ability, are scarcely damaged in the waste water, and can grow in the severe environment of the waste water. That is, the microorganisms having resistance to many antibiotics and assimilability to various saccharoses can probably successfully grow even in the severe environment.
Thus, the bacteria having the TCE degrading ability and more practically advantageous characteristics than the conventionally known bacteria are strongly required.
Furthermore, in biodegrading chlorinated organic compounds such as TCE, tetrachloroethylene (PCE) and dichloroethylene (DCE) in an environment of a polluted site such as a polluted soil, i.e., an open system, the density of the administered microorganisms by which the biodegradation can be carried out is noticeably decreased owing to predation by protozoans and under the influence of other native bacteria. For this reason, it is often very difficult to increase the density of the microorganisms in compliance with a required treatment ability. In order to increase the density of the microorganisms, there are a method which comprises feeding air to the soil, and a method which comprises forwarding a nutritious solution under pressure. However, although requiring a great deal of energy, these methods cannot effectively increase the number of the bacteria per unit area, and so the treatment ability of these methods remains at a low level on the whole.
In the treatment in a reactor or the like, i.e., in the treatment in a closed system, a good deal of energy for nutrient feed and aeration is also required so as to maintain the density of the microorganisms, as in the above-mentioned open system.
The microorganisms which can degrade the chlorinated organic compounds express an enzyme capable of degrading these compounds, but in order to express this kind of enzyme, an inducer is necessary.
In this case, when a large amount of the inducer is used, the degradation activity of the microorganisms increases, and this fact is known only in an example of tryptophan (WO 90/06901). However, detailed reports regarding the amount of the inducer to be used have not been present at all.